A fuel cell is composed of a stack of individual electrochemical cells connected electrically in series and which, each, develop a certain voltage, in general of around 1 volt. The total voltage developed by the stack is therefore equal to the sum of the individual voltages, for example around 100 volts or a few hundred volts for fuel cells targeting applications in the transport field.
Each individual electrochemical cell is usually composed of the superposition of five layers: a polymer film of which one zone forms an ion-exchange membrane, two electrodes comprising chemical elements necessary for the development of the electrochemical reaction, such as for example platinum, and two gas diffusion layers that make it possible to ensure a homogeneous diffusion of the gases transported by the networks of bipolar plates over the whole of the surface of the ion-exchange membrane.
The supply of the gases is ensured by plates that are generally referred to as “bipolar plates” as they are in contact with the anode of one cell and with the cathode of the adjacent cell. Usually, the bipolar plates are composed of an electrically conductive material as it is necessary to ensure an electrical conduction from one cell to the other, the fuel cell being formed by individual electrochemical cells which are connected electrically in series.
Patent Application WO 2005/006472 describes a fuel cell conforming to the above description. FIG. 7, in particular, will be consulted, which shows a stack of individual cells. When the constituent material of the bipolar plates is an electrical conductor, as is most commonly the case, the visible faces of a fuel cell therefore have a voltage when the fuel cell is in service. On one side of the stack, this voltage may become very high, the maximum voltage being the nominal voltage of the fuel cell, namely, typically, greater than 100 volts. It is therefore necessary to encapsulate such a fuel cell to avoid any risk of accidental contact with the latter. This meets both a safety objective and an objective of proper functioning of the cell, as, if the cells were short-circuited, the functioning of the cell would be impaired.